1. Field of the Invention
This invention relates to a method for testing timbers for decay and to equipment for use in such a process.
2. Brief Description of the Prior Art
Timbers for long duration external use such as, for example, utility poles or railway sleepers often have a predictable life span. However, despite a usual initial treatment with a coal tar creosote or a like product the presence of cracks in individual timbers may eventually allow the ingress into the interior of a timber of decay inducing organisms, such as fungi. Since it is clearly uneconomic and disruptive to replace or treat timbers without prior knowledge of the extent of decay, if any, of each timber it is necessary to identify decayed timbers "in situ" and by a non destructive means of testing, so that they may be replaced or treated individually with minimal disturbance.
The present invention relates generally to a method for testing timbers by causing vibrations in the timber and detecting the vibrations so as to identify characteristics associated with the passage of the vibrations through decayed timber. Methods of the above type have been proposed previously.
According to one such method, described in British Pat. No. 1153238, a sonic transducer is placed on the surface of the timber at a point opposite to the point at which the vibration is generated, a filter circuit connected to the transducer divides the signals so detected into preselected high and low frequency segments and the energy in the two segments is compared on the basis that in decayed timber the majority of the energy will be in the low frequency segment.
According to a further such method, described in British Pat. No. 1175719, pulses of accoustical energy transmitted through a pole are compared with those transmitted through a known defect and rot-free pole of the same timber, a longer pulse duration and/or a lower frequency being taken to be indicative of the presence of decay.